Process for the manufacture of alkyl carbonates



@sto M 9 19260 MIXING TUBE FOR CARBON Ma/vox/ma 4N0 CHLOE/NE:

Original Filed July 14, 1924 REF'L X CONDEN SEE REflCT/ON COLUMN FOP? FORMING ETH VL. CHLOE CHRBO/VHTE Patented Oct. 19, 1926.

UNITED STATES PATENT" OFFICE.-

.ronn A. s. HAMMOND, or woonLAwn, MARYLAND, ASSIGNOR TO U. s. INDUSTRIAL ALCOHOL co, A CORPORATION or WEST VIRGINIA.

PROCESS FOR THE MANUFACTURE OF ALKYL .CARBONATES.

Original application filed July 14, 1924, SerialNo. 726,057. Divided and this application filed March 23,

- 1925. Serial No. 17,470.

which is .of such a character as to make the.

manufacture thereof commercially practicable so that the said products will be available for and capable of use in the various arts. It is to be understood, however, .that my process is applicable particularly to the production of alkyl carbonates which are in the same aliphatic'series with diethyl carbonate. The object of my invention is to provide a process for the production of alkyl carbonates, and particularly diethyl carbonate, by means of which the desired product may be produced commercially in an advantageous and economical manner;

Inasmuch as this application is a division of my application upon alkyl carbonate manufacture, Ser, No. 726,057, filed July 14,

1924, the object of my invention is to produce alkyl carbonates in an advantageous manner in accordance-with the process as set forth in said application. Again, a further object is to separate the diethyl carbonate from the reaction mixture with the aid of inert solvents such as a1iphatic hydrocarbons or chlorinated aliphatic hydrocarbons. as, for example, carbon tetrachloride, chloroform, etc., thus obtaing a complete separation of the diethyl carbonate from even large amounts of alcohol. The particular advantage of this procedure is that the carbon tetrachloride does not form a constant boiling mixture with the diethyl carbonate and, therefore, .may. be readily removed from the same by distillation. This has the further advantage, also,

that carbon tetrachloride will abstract even While my invention is capable of being carried out in many different ways I have described only certain ways of carrying out the same hereinafter and while it is capable of being conducted in many diflerent types small amounts ofv diethyl carbonate from the of apparatus I have shown only one type of apparatus to be used, in the drawings in which- The-figure is a diagrammatic representation of an apparatus .Which may be used in accordance with my invention.

Phosgene may be formed in any suitable way,-as, for example, by bringing carbon monoxide and chlorine together in a tube 1 bymeans of branch supply tubes 2 and 3 provided for carbon monoxide and chlorine respectivelyrthe two gases being brought together in the proportions of mol for mol. Thence the gases pass over a suitable catalyst, as, for example, activated charcoal 4 in a chamber 5 surrounded by a cooling jacket 6 and supplied with a current of cooling water, the temperature being kept down to a point preferably below 250 0., a thermometer 7 being provided for this purpose as the reaction is exothermic. Thereafter the phosgene and admixed gases pass out through a tube 8 to the lower end of a column 9 filled with glass beads, which is cooled by a coil 10 supplied witha current of water. In the column 9 the phosgene is brought into contact with a current of absolute alcohol supplied from a tank 11 by means of a tube 12 to the top of the column. Preferably the absolute alcohol is supplied in the 'ratio of 240 grams of the same to 224' grams of phosgene so as to provide an excess of 15% of the ethyl alcohol above the theoretically required amount for the production of diethyl carbonate although it is to be understood that a larger or smaller excess of alcohol may be present if desired.

The temperature of'the column 9 is kept below 40 C., a thermometer 13 being provided for this purpose, The reaction mix- 'ture is then run by a trapped pipe 14 into a flask 15 provided with a thermometer 16 and having a refluxcondenser 17 connected 1 thereto and heat is'supplied from a burner '18 to the flask 15 so as to change the ethyl chlorocarbonate which has been formedm the tower 9 todiethyl carbonate. Refluxing is desirable for this purpose when the alcoholic concentration does not exceed above the theoretical amount of alcohol required in the reaction of forming diethyl carb'onate. Preferably the, reaction mixture is, therefore, refluxed from the. flask 15 for a period of approximately 16 hours at approximately between 50 to 55 C. The time may be cut down by increasing the temperature up to the boiling point of diethyl carbonate, namely 126 C. The hydrochloric acid escapes from the top of the reflux condenser 17 through a tube 19. Inasmuch, however, as ethyl chlorocarbonate is entrained with the hydrochloric acid at the beginning when the free hydrochloric acid concentration is at the highest point,' that is to say amounting to the refluxing is preferably started at 45 C. and kept at this temperature for approximately 2 hours after which the temperature is raised to from 50 to 55 C. and run carefully for 16 hours. The time may be out down b increasing the temperature up to the boiling point of diethyl carbonate, namely 126 C. Therefluxing conducted for this period of time results in reducing the free hydrochloric acid to 5.3% while the combined hydrochloric acid in the form of ethylchlorocarbonate is only 1.8%. Continued refluxing for 7 hours longer converts all of the ethyl chloro carbonate to diethyl carbonate and the free hydrochloric acid is reduced to 2.5% at the end of that period. The final reaction mixture contained in the flask 15 may then be from the following comparison:

c. c. of the reaction mixture containing 10%' removed and treated for the separation of the diethyl carbonate from the other substances present, such as alcohol and hydrochloric acid. For example, the reaction mix-' ture may contain from 50 to 90% of the ester, 2 to 12% of the hydrochloric acid and the remainder alcohol. The separation of the diethyl carbonate from the other constituents contained in the reaction mixture will be more effective in the case where only a slight excess of alcohol hasbeen used over the theoretical amount required to combine with the phosgene. This is especially important inasmuch as diethyl carbonate and ethyl alcohol are difiicult to separate merely by distillation. The advantage ofv using only a slight excess of alcohol is a parent en 110 ethyl alcohol and 90% diethyl carbonate is washed with 110 c. c. of water, an oil layer of 100 c. c. will separate, comprising 97.2% of the ester present in the two layers, while if the alcoholic concentration is 50% in excess the ester layer which will separate will contain only 55 c. c. and the percentage of the ester in the oil layer will be onl 79.6% of the ester in the two layers. For t is purpose, therefore, the wei hed portion of the reaction mixture may 5 titrated with normal sodium hydroxide solution in water and the amount ofcaustic solution to be added to the mixture is calculated therefrom as bein sufiicient for neutralizing the free hydrochiiric acid, the caustic soda solution to be added being diluted with water to ,a 20% strength solution before being added.

been present with the ester layer will have been removed. The addition of the 20% caustic solution in this way neutralizes some of the acid immediately but most of the neutralization takes place during the agitationwhich requires from 4 to 8 hours. It is found, also, that a 20% caustic soda solution will notinix with the reaction mixture. The salt water layer will be found to contain the sodium chloride formed from the neutralization and less than of 1% of ester. If desired, the upper water layer may be subsequently rectified by distilling the same after removal from the water layer.

For the purification, however, if desired, instead, the contents of the flask- 15 may be subjected to a somewhat different treatment .for the separation of the diethyl carbonate therefrom by subjecting the same to extraction with inert solvents in the form of aliphatic hydrocarbons or chlorinated derivatives thereof, as, for example, carbon tetrachloride, chloroform or petroleum ether and, in fact, any diethyl carbonate solution containing alcohol may be separated in this way. For example, in the case where the solution contains 50 c. c. of absolute alcohol and 50 c. c. of diethyl carbonate, 50 c. c. of carbon tetrachloride is added and the mixture shaken, and there may then be added 100 c, c. of water and the mixture again shaken. As a result two liquid layers are formed, the lower layer containing diethyl carbonate and carbon tetrachloride showing an increase of 50 c. c. corresponding to the amount of diethyl carbonate added originally. This lower layer may then be removed and distilled to separate the diethyl carbonate from the carbon tetrachloride by fractionation. The carbon tetrachloride distills over between 66 and 79 (3., 50 c. 0. being recovered. Also 2 c. c. of diethyl carbonate distills between 50 and 122 C. and 47 c. c. distills be- 1 tween 123 and 127 C., the last mentioned fraction being comprised of 94% diethyl in detail I wish it to be understood that many changes may be made therein without,

after in the form of a liquid ali hatic compound which in the presence water acts as a non-solvent for the alcohol layer formed and adding water to the solution to form separateliquid layers.

2. The process which comprises forming a dialkyl carbonate in a rection mixture containing phosgene and an aliphatic alcohol and recovering the carbonate from thereact1on mixture by the addition of an inert solvent in the form of carbon tetrachloride and addingwater to the rate liquid layers.

3. The process which comprises reacting upon an aliphatic alcohol with phosgene, thus forming an alkyl chlorocarbonate car: rying the reaction farther to produce a dialkyl carbonate involving heat and refluxing and recovering the carbonate from the reaction mixture by the addition of an inert solvent thereafter in the form of a liquid aliphaticcompound which in the presence of w ter acts as a non-solvent for the alcohol ayer formed and adding water to the solution to form separate liquid layers.

4. The process which comprises reacting upon an aliphatic alcohol with phosgene, thus, forming an alkyl chlorocarbonate carsolution to form separying the reaction farther to produce a dialkyl carbonate involving heating and refluxing and recovering the carbonate from the reaction mixture by the addition of an' inert solvent in the form of carbon tetrachloride and adding water to the solution to form separate liquld la ers.

5. The process whic comprises reacting upon an aliphatic alcohol with phosgene, thus forming an alkyl chlorocarbonate carrying the reaction farther to produce a dialkyl carbonate and recovering the carbonate from the reaction mixture by the addition of an inert solvent thereafter in the form of a liquid aliphatic compound which in the presence of water acts as anon-solvent for the alcohol layer formed, adding water to l the solution to form separate liquid layers and distilling the ester containing layer to separate theester from the solution by fractionation.

6. The process which comprises reacting upon an aliphatic alcohol with phosgene,

thus forming an alkyl chlorocarbonate carrying. the reaction farther to produce a dialkyl carbonate and recovering the carbonate from" the reaction mixture by the addition of an inert solvent in the form of carbon tetrachloride, adding water to' the solution to form-separate liquid layers and dis tilling the ester containing layer to separate the ester from the solution by fractionation.

7. The process which comprises reacting upon alcohol with phosgene, thus forming.

ethyl chlorocarbonate carrying the reaction farther to produce diethyl carbonate involving heating and refluxing and recovering the carbonate from the reaction mixture by the addition of an inert solvent thereafter in the form of a liquid aliphatic compound a which in the presence of water acts as a non solvent for the alcohol layer formed and addm water to the solution to form separate llquid layers;

8. The process which comprises reacting uponalcohol with phosgene, thus forming ethyl chlorocharbonate carrying the reaction farther to produce diethyl carbonate and recovering the carbonate from the reaction mixture by-the addition of an inert solvent in the formof carbon tetrachloride and adding water to the'splution to form separate llquid layers. 4

9. The prbc'ess which comprises, reacting.

upon alcohol with phosgene, thus. forming ethyl chlorocarbonate carrying the reaction farther to produce diethyl carbonate involving heatin and refluxing and recovering the carbonate from the reaction mixture bythe addition of an inert solvent thereafter in the form of a liquid aliphatic compound, which in the presence of water acts as a non-solvent for the alcohol layer formed, adding water to the solution to form separate liquid layers and distilling the ester'containing layer to separate the fractionation. I

10. The process which comprises reacting upon alcohol with phosgene,thus forming ethyl chlorocarbonate carryin the reaction farther to reduce diethyl car onate and recovering t e carbonate from the reaction mixture by the addition of an inert solvent in the form ofcarbon tetrachloride, addingv water to the solution to form separate liquid layers and distilling the ester containing ayerto separate the ester from the solution by fractionation.

In testimony that I claim the foregoing, I have hereunto set myhand this 17th day of March, 1925.

-' JOHN A. S. HAMMOND.

ester from the solution by 

